Recently, a hybrid vehicle equipped with an engine for outputting torque by burning of fuel and an electric motor for outputting the torque by supply of electricity and capable of driving by transmitting the torque of the engine and the electric motor to wheels is suggested. In such a hybrid vehicle, the wheels are driven only by the torque of the electric motor or driven by the torque of both the engine and the electric motor, by controlling driving and stopping of the engine and the electric motor according to driving condition, and the electric motor can be driven by electricity stored in a battery and when the energy of the battery decreases, the battery is charged by driving the engine.
That is to say, the hybrid vehicle is provided with the engine and the electric motor as a drive power source and with a planetary gear for combining the power of the engine and the electric motor to transmit to the wheels. Specifically, it is configured such that an output shaft of the engine is coupled to a carrier of the planetary gear and an output shaft of the electric motor is coupled to a ring gear of the planetary gear, and the power is transmitted from a sprocket coupled to the ring gear to the wheels. Also, an electricity generator is provided between the planetary gear and the engine, and a rotating shaft of the electricity generator is coupled to a sun gear of the planetary gear. Therefore, the power of the engine is divided to the wheels and the electricity generator by the planetary gear, and by controlling a rotation speed of the electricity generator, the rotation speed of the engine can be controlled. That is to say, a power dividing mechanism composed of the planetary gear has a function of converting the rotation speed of the engine and a function of dividing the power of the engine to the wheels and the electricity generator.
In the hybrid vehicle, when a driver operates an auto cruise switch to perform constant-speed driving, the drive of the engine and the electric motor is controlled such that the target vehicle speed for performing the constant-speed driving is set and deviation between the current vehicle speed and the target vehicle speed is reduced. That is to say, the vehicle is stably driven at the target vehicle speed by calculating energy in a direction to negate the deviation between the current vehicle speed and the target vehicle speed to increase and decrease the torque of the engine and increase and decrease the torque of the electric motor.
Meanwhile, such a vehicle driving control apparatus is disclosed in Patent Documents 1 to 5.
Patent Document 1: Japanese Patent Application Laid-Open No. H07-047862
Patent Document 2: Japanese Patent Application Laid-Open No. H10-309959
Patent Document 3: Japanese Patent Application Laid-Open No. H08-282328
Patent Document 4: U.S. Patent Application Publication No. 2007/255477 Specification
Patent Document 5: Japanese Patent Application Laid-Open No. 2000-43611